Document Type

    Article

    Publication Date

    9-14-2012

    Publication Title

    The Journal of Biological Chemistry

    Abstract

    Gram-negative bacteria harboring KPC-2, a class A β-lactamase, are resistant to all β-lactam antibiotics and pose a major public health threat. Arg-164 is a conserved residue in all class A β-lactamases and is located in the solvent-exposed Ω-loop of KPC-2. To probe the role of this amino acid in KPC-2, we performed site-saturation mutagenesis. When compared with wild type, 11 of 19 variants at position Arg-164 in KPC-2 conferred increased resistance to the oxyimino-cephalosporin, ceftazidime (minimum inhibitory concentration; 32→128 mg/liter) when expressed in Escherichia coli. Using the R164S variant of KPC-2 as a representative β-lactamase for more detailed analysis, we observed only a modest 25% increase in kcat/Km for ceftazidime (0.015→0.019 μm−1 s−1). Employing pre-steady-state kinetics and mass spectrometry, we determined that acylation is rate-limiting for ceftazidime hydrolysis by KPC-2, whereas deacylation is rate-limiting in the R164S variant, leading to accumulation of acyl-enzyme at steady-state. CD spectroscopy revealed that a conformational change occurred in the turnover of ceftazidime by KPC-2, but not the R164S variant, providing evidence for a different form of the enzyme at steady state. Molecular models constructed to explain these findings suggest that ceftazidime adopts a unique conformation, despite preservation of Ω-loop structure. We propose that the R164S substitution in KPC-2 enhances ceftazidime resistance by proceeding through “covalent trapping” of the substrate by a deacylation impaired enzyme with a lower Km. Future antibiotic design must consider the distinctive behavior of the Ω-loop of KPC-2.

    Comments

    This work was supported, in whole or in part, by National Institutes of Health Grant 1R01-A1063517 (to R. A. B.).

    Creative Commons License

    Creative Commons Attribution 4.0 International License
    This work is licensed under a Creative Commons Attribution 4.0 International License.

    DOI

    10.1074/jbc.M112.348540

    Version

    Publisher's PDF

    Volume

    287

    Issue

    38

    Download

    Share

    COinS